1. Field of the Invention
The present invention relates to a zoom lens and an image pick up apparatus including the zoom lens and is suitable for use in, for example, an electronic camera such as a video camera or a digital still camera, a film camera, and a broadcast camera.
2. Related Background Art
Up to now, an example of a zoom lens used for a photographic camera such as a film camera or a digital still camera or a video camera includes a zoom lens employing a so-called rear focus system, in which lens units located in the rear of (closer to an image side than) a first lens unit closest to an object side are moved for focusing.
The zoom lens of the rear focus system is disclosed in each of Japanese Patent Application Laid-Open Nos. H06-148523, H08-005913, H08-146295, and Japanese Patent Publication No. S39-029046.
The zoom lens disclosed in the patent documents includes a first lens unit having positive refractive power, a second lens unit having negative refractive power, a third lens unit having positive refractive power, a fourth lens unit having negative refractive power, and a fifth lens unit having positive refractive power, which are disposed in order from the object side to the image side. Zooming is performed using the five lens units. The zoom lens is a zoom lens having a high-zoom ratio.
Note that the “refractive power” described in the specification of this application indicates optical power of a lens element or a lens unit and corresponds to the reciprocal of a focal length thereof.
In the zoom lens disclosed in Japanese Patent Application Laid-Open No. H06-148523, the second lens unit, the third lens unit, and the fourth lens unit are moved for zooming. The zoom lens has a zoom ratio of approximately 10 times and an F-number of approximately 2.0. In the zoom lens, an aperture stop is moved independently of the moved respective lens units during zooming.
In the zoom lens disclosed in Japanese Patent Application Laid-Open Nos. H08-005913 and H08-146295 (corresponding to U.S. Pat. No. 5,847,882 and U.S. Pat. No. 6,094,312), an aperture stop is disposed between the second lens unit and the third lens unit. During zooming from a wide-angle end to a telephoto end, the second lens unit is moved toward the image side and the fourth lens unit for focusing is moved. However, the aperture stop is fixed in the zoom lens and thus it is not moved during zooming.
In the zoom lens disclosed in Japanese Patent Publication No. S39-029046, the second lens unit and the fourth lens unit are moved during zooming from the wide angle end to the telephoto end. The zoom lens has a zoom ratio of approximately 4.2.
In recent years, with a reduction in size of an image pick up apparatus and an increase in resolution of an image pick up element, a zoom lens whose zoom ratio is high and in which a size of the entire lens system is small has been required as a zoom lens used for a digital camera, a video camera, and the like.